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N-Acetyltransferase 2 (NAT2) metabolizes arylamines and hydrazines. The substrates of NAT2 include many therapeutic drugs, such as isoniazid (INH), as well as chemicals and carcinogens (1)(2)(3). For that reason, N-acetylation activity is associated with drug effects or toxicities and susceptibility to various cancers. The ability of NAT2 to N-acetylate arylamines is subject to a genetic polymorphism in the NAT2 gene. The acetylation rate and NAT2 genotype distribution are quite different among various populations. The genetic polymorphism in NAT2 has not been studied extensively in the Korean population. Previous reports were based only on phenotyping or restriction fragment length polymorphism analysis, leading to possible misclassification of genotypes. We therefore decided to investigate NAT2 allelic variability and genotype distributions in the Korean population by complete sequencing. We also evaluated the relationship between genotype and phenotype to understand N-acetylation pharmacogenetics.

One thousand Korean individuals who visited the health promotion center at Samsung Medical Center were anonymously studied. An additional 23 healthy volunteers and 18 patients with pulmonary tuberculosis participated in this study. DNA was extracted from peripheral blood leukocytes. We amplified a 1211-bp fragment that included an 870-bp protein-coding region of the NAT2 gene and performed full sequencing analysis (4) on an ABI Prism 377 DNA Sequencer (Perkin-Elmer). We then checked nucleotide substitutions by combined use of allele-specific-PCR (AS-PCR) and restriction enzyme digestion. Specific primers (5) for the wild-type and mutant alleles were used in separate PCRs to detect C282T, T341C, and G590A substitutions. The nucleotides at positions 190, 481, 590, 803, and 857 were explored by digesting the 1211-bp PCR fragment or AS-PCR product carrying the wild-type or mutant allele with NciI, KpnI, TaqI, DdeI, and BamHI, respectively. For phenotyping, the healthy volunteers and patients gave informed consent and were given 300 mg of INH orally after an overnight fast. Participants were 18–65 years of age; had no underlying liver, kidney, or gastrointestinal diseases; did not have any drug history within the previous 2 weeks; and were not chronic alcoholics. Blood samples were obtained at 6 h, and urine samples were collected up to 6 h after INH administration. We measured urine and plasma concentrations of INH and acetylisoniazid (AcINH) by HPLC (6), using a Hewlett Packard 1090 HPLC with an ultraviolet detector. The plasma concentration ratio of AcINH to INH (pAcINH/INH) and the urinary molar ratio of INH to AcINH (uINH/AcINH) were calculated. We applied the χ2 test and the Fisher exact test for categorical variables and the Mann–Whitney test or Kruskal–Wallis test for numerical variables.

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